This application seeks support for a training program that prepares highly qualified pediatricians and selected Ph.D. postdoctoral scientists to assume leadership positions as investigators in Pediatric Infectious Diseases. Based in the Division of Infectious Diseases at Children's Hospital Boston, the program takes advantage of the rich academic and research resources of Harvard Medical School, Harvard School of Public Health, and affiliated teaching hospitals to bring together outstanding didactic experiences and research opportunities relevant to infectious diseases of children. Support for a total of six positions per year is requested (four M.D. and two Ph.D.). Pediatricians enter the program for a minimum of three years of integrated clinical and research training that includes at least two years of supervised research under the mentorship of a member of the teaching faculty. Research training of pediatricians is fully integrated with that of Ph.D. postdoctoral trainees in the laboratories of the teaching faculty. The 23 members of the teaching faculty are accomplished investigators and experienced mentors chosen from the Division of Infectious Diseases at Children's Hospital Boston and five affiliated units at other Harvard institutions. Under the guidance of the research mentor and the Program Steering Committee, an individualized curriculum is designed for each trainee in one of three broad areas of investigation: microbial pathogenesis, host response and vaccines, or epidemiology and health policy. Trainees in the epidemiology and health policy pathway have the opportunity to earn a Master's of Public Health degree from the Harvard School of Public Health as an integral part of the training program. Trainees in the other pathways also receive training in epidemiology, biostatistics, clinical trial design, and analytic methods. All trainees have seminars and tutorials in grant preparation and scientific writing that supplement the mentored research experience. An individual Scholarship Oversight Committee is appointed for each trainee to monitor progress and to provide career guidance. During the second or third year, trainees are expected to present their work at national meetings, to prepare one or more manuscripts for publication, and, in most cases, to apply for a K08 or other career development award to support the transition to independence as an investigator. Relevance: The goal of the training program is to train pediatricians and Ph.D. postdoctoral scientists for careers as researchers who will address the present and future challenges of childhood infections. Well- trained investigators in Pediatric Infectious Diseases are urgently needed to meet the ongoing and emerging threats to child health of congenital HIV infection, childhood malaria and tuberculosis, diarrheal diseases, and respiratory infections-critical problems that are further complicated by increasing antimicrobial resistance and societal opposition to childhood vaccines.